1. Field of the Invention.
This invention relates to public key cryptographic techniques, and more specifically to systems for one party to convince another, including signatures.
2. Description of Prior Art.
Included here by reference are the following and any related patents, applications, and publications: U.S. Pat. No. 4,947,430, titled "Undeniable signature systems," issued Aug. 7, 1990, to the present applicant, also as European publication 88202620.6; and U.S. application Ser. No. 08/066,669 titled "Designated confirmer signature systems."
Previously disclosed undeniable and designated confirmer signature systems, such as those referenced above, use an exchange of messages between the signer and the recipient, interactively in both directions, during the process of providing a signature. In some applications, such as electronic mail for instance, there may be advantage in the signer being able simply to form and send a signature without interacting with the recipient.
More generally, in the context of cryptographic techniques, a prover party is typically said to convince or prove something to an intended recipient party. In such situations the prover may desire to prevent others, apart from the intended recipient(s), from being convinced.
With signatures as well as more general proofs, the use of interaction as a way to limit a recipient to a single party determined by the prover may not be effective. If the intended recipient wishes to allow other parties to be convinced--even against the wishes of the prover it may be possible if the others cooperate in forming the challenge during the interaction.